The present invention relates to an inner cable. More particularly to an inner cable composed of a core and N pieces of strands wound around the core, characterized in that in each diameter of M (1.ltoreq.M.ltoreq.0.3N) piece(s) of strands of the N pieces of strands is larger than that of remaining (N-M) pieces of strands, where the above-mentioned N.gtoreq.4 and M are integers.
Conventionally, previous inner cables being used as push-pull control cables have been configured to comprise a core b and a plurality of strands c spirally wound around the core b. For example, as disclosed in FIGS. 3(a) and 3(b) which denote prior art, the core b is composed of a single wire or stranded wires that have a diameter which is identical to each other.
Further, as an inner cable for control cable, there has been such a geared cable composed of a core and a -strand having relatively large diameter, the strand being spirally wound around the core in such a manner as not to contact with each other.
In Japanese Examined Utility Model Publication No. 35787/1985, as shown in FIGS. 4(a) and 4(b), there is disclosed an inner cable for push-pull control cable, the inner cable being composed of a core 31 composed of a single wire or stranded wires, a plurality of main strands 32 spirally wound around the core 31 in such a manner that the plurality of strands 32 are not contacted with each other, and each of the strands 32 is evenly spaced with each other, and a plurality of secondary strands 33 arranged between the above-mentioned main strands, in which diameter of each of the main strands is larger than that of each of the secondary strands.
In Japanese Examined Utility Model Publication No. 11380/1988, as shown in FIGS. 5(a) and 5(b), there is disclosed an inner cable for push-pull control cable, the inner cable being composed of a core 41 and a plurality of strands 42 spirally wound around the core 41, each strand 42 being composed of a plurality of wires stranded with each other, e.g., wound together to form the strand 42. On the plurality of wires, there is formed a covering layer 44 made of synthetic resin, the covering layer 44 including a thick portion 44a and a thin portion 44b.
In Japanese Unexamined Patent Publication No. 26640/1995, there is disclosed a push-pull control cable including: an inner cable 52 composed of a core 53 made of a single steel wire extending straight and having a resilient property, and a plurality of strands wound around the core 53, each of the strands being composed of a plurality of wires; and a conduit, into which the inner cable 52 being inserted.
Conventionally, as a problem to be solved in the push-pull control cable there is generated a noise during an operation of the push-pull control cable or at the time of finishing the operation thereof.
In order to solve the above-mentioned problem, there is such a method as to reduce clearance between outer surface of the inner wire and inner surface of the conduit.
However, in the method there is a problem to deteriorate essential performance of the control cable if the clearance is to be reduced because load efficiency is lowered and sliding resistance with no load is increased.
Comparing with the prior art of FIGS. 3(a) and 3(b), clearance in the prior art of FIGS. 4(a) and 4(b) is large. In the prior art of FIGS. 5(a) and 5(b), coefficient of friction is small since the surfaces to be slided on both ides of the conduit and the inner cable are made of synthetic resin. In the prior art of FIG. 6, there is employed a strand construction wherein each strand is composed of a plurality of wires. Therefore, when the clearance is small, decreasing of the load efficiency is small, but the load efficiency cannot be satisfactory.
The object of the present invention is to provide an inner cable in which the load efficiency is not lowered, the sliding resistance with no load is not increased, and any noise is not generated in the operation of the push-pull control cable.